National and college-based epidemiological studies provide strong evidence that nonmedical prescription drug use is increasing among U.S. college students (e.g., Johnston et al., 2003; Mohler-Kuo et al., 2003). However, nonmedical prescription drug use has received scant attention and little epidemiological research exists that adequately assesses the characteristics of those individuals most at risk for nonmedical use of abusable prescription drugs. Thus, the broad, long-term objectives of the proposed research are to document longitudinal trends and risk factors associated with nonmedical prescription drug use among U.S. college students. The proposed secondary analyses will utilize the "Study of College Health Behaviors" (Wechsler et al., 2002), which collects cross-sectional data on five independent national samples of over 10,000 U.S. college students each year (1993, 1997, 1999, 2001, and 2004); the focus will be on the nonmedical use of prescription drugs including opiate analgesics, sedative/anxiolytics, and stimulant medications for attention deficit hyperactivity disorder (ADHD). The specific aims are: 1) to assess the prevalence and longitudinal trends of nonmedical use of prescription drugs among U.S. college students between 1993 and 2004; 2) to examine the student-level and institutional-level characteristics that are associated with increased risk for nonmedical prescription drug use; 3) to compare the age of initiation for nonmedical prescription drug use to the ages of initiation for alcohol, marijuana and other drug use as well as investigate the relationship between age of initiation for nonmedical prescription drug use with the prevalence of past year substance abuse and dependence; 4) to examine the association between nonmedical prescription drug use and other drug use at the college-level, and to explore the association between nonmedical and medical use of prescription drugs. Several multivariate statistical analyses will be used to examine the longitudinal trends in the prevalence rates and risk factors associated with nonmedical use. Findings from this research will have important implications for the understanding of the epidemiology, prevention and treatment of prescription drug abuse.